X-ray fluoroscopic analysis



Jan. 22, 1963 A. A. TABlKH X-RAY FLUOROSCOPIC ANALYSIS 2 Sheets-Sheet 1 Filed Oct. 4, 1960 mmkzbbb INVENTOR. ALI A. TABIKH ATTORNE vs Jan. 22, 1963 A. A. TABIKH 3,075,079

X RAY FLUOROSCOPIC ANALYSIS Filed Oct. 4, 1960 2 Sheets-Sheet 2 ;-0/ X SJNHOD 7710i AL! A. TABIKH BYWILW';

A'T TORNE VS United States Patent 3,075,079 X-RAY FLUORGSCOPIC ANALYSIS Ali A. Tabikh, Riverside, Calif., assignor to California Portland Cement Co., Los Angeles, Calif., a corporation of California Filed Oct. 4, 1964 Ser. No. 60,424 6 Claims. (Cl. 250-515) This invention relates generally to X-ray fluorescence spectrographic analysis and more particularly concerns the obtaining of significantly improved analytical data especially as regards quantitative elemental analysis of specimens through the use of this type equipment.

The application of X-ray fluorescence analysis for various elements present in material such as Portland cement and cement raw mix, rocks, soils and many other substances appears to be quite promising. One of the major difficulties, however, in X-ray fluorescence analysis of such materials, where low atomic number elements are concerned (atomic number 20 and below), is matrix inhomogeneity in the sample. Such inhomogeneities arise because each of these materials is generally composed of a number of minerals in various crystalographic forms and sizes as Well as amorphous particles of differing shapes and finenesses. Therefore, every sample of raw mix or any other substance mentioned above inevitably contains a heteropolymorphic surface and matrix. For this reason, every time a sample of the above mentioned materials is placed in the path of a primary X-ray beam it represents, at least microscopically or submicroscopically, a specific surface geometric orientation. This is likely to change with successive removals and replacements of the sample or during analysis of several samples of the same substance.

Surface heterogeneity in a given sample is especially undesirable for the analysis of light elements. This is due to the susceptibility of the characteristic radiations from light elements to be absorbed difierently by different elements, or crystalline structure, or particle orientations on the surface of the sample; hence, correlation becomes poor or is lacking between chemical analysis and X-ray fluorescence analysis when the specimens to be analyzed possess surface and/0r matrix heteropolymorphic characteristics.

As a solution to the above mentioned ditliculties, the present invention contemplates that improved results may be obtained by or through the process of detecting a quantity of fluorescent radiation leaving the specimen over an interval of time, while creating relative movement between the specimen and the path of radiation incident thereon during the detection time interval. The time interval referred to is made suflicient that the detection continues while the surface irregularities of the specimen are presented in many different orientations to the incident radiation so that if, for example, the specimen is rotated during the detection time interval, the sum of all possible surface (or matrix) geometric particle orientations will have been exhibited. As a result, the accuracy of quantitative analysis through X-ray or electron probe fluorescence spectrographic technique is greatly enhanced. This is particularly true as regards raw mix samples to be subjected to kiln treatment in cement production, since such raw mixed samples contain comminuted minerals and/ or oxides of low atomic number elements including calcium, aluminum, iron and silicon.

These and other objects and advantages of the invention as well as the details of illustrative embodiments thereof will be more fully understood from the following detailed descriptions of the drawings in which:

FIG. 1 is a diagrammatic showing of the spectrographic equipment used in practising the invention;

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FIG. 2 is a view taken on line 22 of FIG. 1; and

FIG. 3 is a graph illustrating the improvements obtained as a result of practising the invention, particularly as regards quantitative analysis of typical specimen.

Referring first to FIG. 1, there is shown therein an arrangement of components for fluorescent X-ray spectroscopy, these components including the primary X-ray tube 10, the specimen 11, the collimator 12, an analyzing crystal 13, and a detector 14.

The primary X-rays from the tube 10 are indicated at 15, and they strike the specimen 11 generating the characteristic X-ray fluorescent radiations of the specimen elements. These fluorescent radiations are emitted from the specimen in all directions, and it is the function of the collimator 12 to limit these characteristic X-rays to a point or line source shown at 16, the characteristic rays being shown or indicated at 17.

Next, the rays 17 strike the analyzing crystal 13 and for each angular setting of the latter, only one wave length will be reflected according to the Bragg law:

In the latter well known equation, n is the order of diffraction; is the wavelength in Angstroms; d is the interplanar spacings of the crystal in Angstroms; and 0 is the angle between the incident radiation and the crystal surface. The reflected radiation emerges at an angle 20 with respect to the incident beam and is measured by the detector 14, such radiation being indicated at 18. The wavelengths of the measured X-ray lines determine the elements present in the specimen and the intensity of each line is related to the percentage composition of that element. Typically, the detector 14 comprises a radiation counter such as a gas flow proportional counter tube receiving radiation through the slit 19 in the collimator 20. To determine the intensity of the radiation during a particular time interval, the switch 21 is closed to establish a circuit running from the detector 14 to a suitable counter 22. Accordingly, if two different specimens have lesser and greater concentrations of a particular element such as calcium, the counter will record lesser and greater radiation counts over equal counting intervals established by closing the switch 21.

In accordance with the invention, relative movement is created between the specimen 11 and the path of the incident radiation 15 during the detection time interval previously referred to. Typically, but not necessarily, the specimen is caused to rotate in the path of the incident radiation. If the sample is solid, it may be carried or supported in a holder such as the cup-shaped receptacle 23 which is supported by a shaft 24 driven in rotation by suitable means such as a motor 25. Starting and stopping of the motor and also the speed thereof may be suitably controlled manually by the mechanism shown at 26, which includes a manual control 27.

As the sample is rotated around an axis normal to its surface, at any instant it possesses surface (also matrix) geometric particle orientations:

. 1: 2: 3 n-l: n corresponding to sample positions:

along the path of rotation, n representing the final positional setting in completing one full rotation. It is clear that when one full rotation is completed the sum of all possible surface geometric particle orientations will have been exhibited. Therefore, it follows that:

where H is the sum of all possible surface (also matrix) geometric orientations in a sample.

While no one given it is reproducible from sample to sample, it is believed that H can be adequately reproduced by rotation. If a sampleis placed under a primary X-ray or electron beam and is kept in a rotary motion on an axis normal to the surface which is being bombarded by X-rays, H will bereproduced as many times as the number of rotations during a specific period of time. This will be reproduced every time the sample is removed and put back in its place. It will also be reproduced within a group of samples made from common parent material and having approximately similar chemical compositions. In other words, an efiective matrix homogeneity is produced by rotation. Therefore, rotation of the samples during X-ray fluorescence (spectrographic) analysis should overcome the poor or lack of correlation and reproducibility when analyzing for elements particularly those of low atomic number in such materials as Portland cements and cement raw mix, rocks, soils and many other substances. On this basis X-ray fluorescence (spectrographic) analysis is rendered fully applicable to the quanti- M tative determinations of elements mentioned above.

A typical raw mix sample has the following analysis:

present in materials as Percent CaO a 42.8 SiO 14.5 A1 2.0 F6203 1.6 MgO I 3.5 Combustion loss (Q0 If the sample is held stationary with respect to the incident radiation 15, the latter falls within the shaded rectangular zone indicated at 28 in FIG. 2, the specimen being shown at 11, and the zone 28 being centered within the specimen. The axis of rotation of the specimen is shown at 24. On the other hand, if the specimen is rapidly rotated during the detection interval, the incident radiation falls within the circle designated in broken lines at 39, since over the detection interval the shaded Zone 1 23 rotates about the center 29.

Referring now to FIG. 3, the graph shown indicates poor between chemical and fluorescent analysis, whereas for the. circular pointsthe correlation is good, as indicated by the line 331' of best fit derived by the least squares method, the coefficient of variationbeing calculated to be $0.917. The equation for the line of regression (line of.

best fit) obtained by the method of least squares is:

Y 19,842.5+l782.9X

Where Y s are the theoretical values corresponding to Ys on the graph.

Accordingly, it is clear that the creation of relative movement between the specimen and the incident radiation during the detection interval achieves significant improvements in X-ray fluorescence spectrographic analysis. This is especially evident wherever and whenever the above mentioned physical as Well as chemical conditions appear in examined specimens.

The described principles of X-ray, or electron probe, fluorescence spectrographic analysis and the application of the invention thereto are to be clearly distinguished from known X-ray diffraction techniques.

E claim:

1. In X-ray or electron probe fluorescence spectrographic analysis, the steps that include forming a specimen of solid comminuted material principally containing oxides of elements having atomic number 20 and less, the specimen being formed to have particle surface heterogeneity, positioning the specimen with the heterogeneous surface thereof presented to incident radiation productive of fluorescent radiation leaving the specimen, detecting a quantity of said radiation leaving the specimen over an interval of time for quantitative elemental analysis, and creating relative movement between the specimen irradiated surface and the path of said incident radiation during said detection time interval, said movement being carried out at a speed such that said detected radiation is efiectively that which would be produced by a specimen having particle surface homogeneity.

2. in X-ray or electron probe fluorescence spectrographic analysis, the steps that include forming a specimen of solid comminuted material principally containing oxides of elements having atomic number 20 and less, the specimen being formed to have particle surface heterogeneity, positioning the specimen with the heterogeneous surface thereof presented to incident radiation productive of fluorescent radiation leaving the specimen, detecting quantities of said radiation of Wavelengths corresponding to said elements leaving the specimen over difierent intervals of time for quantitative elemental analysis, and creating relative movement between the specimen irradiated surface and the path of said incident radiation during said time intervals by rapidly rotating the specimen, said time intervals and relative movement being suflicient that said detection continues while said specimen rotates through at least one full rotation so that said surface heterogeneities arepresented in many different orientations to said incident radiation and said cletected'radiation is effectively that which would be produced by a specimen having particle surface homogeneity.

3. The. method of claim 2 wherein said detection is carried out by approximately totaling the quantity of fluorescent radiation leaving the specimen and arriving within a detection zone during said intervals of time.

4. The method of claim 2 wherein the material contains oxides of calcium, altuninum, silicon, iron and magncsium.

5. The method of claim 2 wherein said specimen comprises Portland cement.

6. The method of claim 2 wherein said smcimen comprises cement raw mix.

References Cited in the file of this patent UNITED STATES PATENTS 2,490,673 Champaygne et al. Dec. 6, 1949 2,602,142 Meloy July 1, 1952 2,901,629 Friedman Aug. 25, 1959 

1. IN X-RAY OR ELECTRON PROBE FLUORESCENCE SPECTROGRAPHIC ANALYSIS, THE STEPS THAT INCLUDE FORMING A SPECIMEN OF SOLID COMMINUTED MATERIAL PRINCIPALLY CONTAINING OXIDES OF ELEMENTS HAVING ATOMIC NUMBER 20 AND LESS, THE SPECIMEN BEING FORMED TO HAVE PARTICLE SURFACE HETEROGENEITY, POSITIONING THE SPECIMEN WITH THE HETEROGENEOUS SURFACE THEREOF PRESENTED TO INCIDENT RADIATION PRODUCTIVE OF FLUORESCENT RADIATION LEAVING THE SPECIMEN, DETECTING A QUANTITY OF SAID RADIATION LEAVING THE SPECIMEN OVER AN INTERVAL OF TIME FOR QUANTITATIVE ELEMENT ANALYSIS, AND CREATIN RELATIVE MOVEMENT BETWEEN THE SPECIMEN IRRADIATED SURFACE AND THE PATH OF SAID INCIDENT RADIATION DURING SAID DETECTION TIME INTERVAL, SAID MOVEMENT BEING CARRIED OUT AT A SPEED SUCH THAT SAID DETECTED RADIATION IS EFFECTIVELY THAT WHICH WOULD BE PRODUCED BY A SPECIMEN HAVING PARTICLE SURFACE HOMOGENEITY. 